In people's production and life, different electric tools are usually needed to complete various tasks. For example, an electric saw is used to perform tasks such as forest harvesting, bucking, branching and wood cutting, an electric drill is used to drill holes, an electric screwdriver is used to tighten or remove screws, and a hand mill is used to perform edging, trimming and polishing on glass and resin. Electric tools are easy to operate and are laborsaving.
FIG. 1 shows a drive circuit for an electric tool in the conventional technology. A trigger switch 90 is needed in the electric tool in the conventional technology to control the electric tool to operate or not. The trigger switch 90 is connected between a power supply 92 and an inverter 94 of the electric tool. When the trigger switch 90 is turned on, the electric tool is in operation, and a drive control circuit 93 outputs a drive signal based on a position of a magnetic field of a rotor detected by a position sensor 99, to control the inverter 94 to convert electrical power of the power supply 92 into alternating current power which is supplied to a motor 95, so that the motor 95 drives a working head of the electric tool to operate. Since the trigger switch 90 is connected between the power supply 92 and the inverter 94 of the electric tool, the trigger switch 90 is required to have a very high rated current. For example, in an electric drill, the rated current may be up to about 10 amperes. In practice, a trigger switch that can withstand a high current is expensive, which increases the cost of the electric tool.